Distributed power generation, in which relatively small electrical generation sources (sometimes known as distributed energy resources or DERs) that may be primarily intended to serve a specific load are interconnected with a larger-scale electrical power grid to enable sharing of excess power that they generate, is coming into increasing use as a way of facilitating the use of renewable energy resources and improving the overall reliability and efficiency of the power grid. A persistent problem in distributed power generation systems, however, is the hazard to personnel and equipment that occurs when a segment of the grid containing a DER becomes unintentionally disconnected from the remainder of the grid containing the primary central generation source. When a segment is disconnected, the DER may continue to power the disconnected segment, forming an “island.” This can endanger personnel who may be working to restore connection of the segment with the grid and may wrongly assume the islanded segment is not energized. Further, voltage or frequency deviations in the islanded segment may damage electrical equipment connected to the segment. For these reasons, industry standards such as IEEE 1547 have been developed that require distributed generators to detect unintentional island formation so that appropriate corrective action can be taken in a timely fashion.
Prior attempts have been made at developing methods for detecting island formation, and have included active, passive, and communications-based methods. None of these prior methods, however, have proven entirely satisfactory. For example, communications-based methods many be ineffective if communications are interrupted before an islanding event occurs. Some of the prior methods rely on complex signal processing techniques, which to be effective, often require the use of expensive, high-powered computational equipment. Other active prior islanding detection methods require the distributed generation system to inject a perturbation with a specific detectable signature. Such methods, however, require specialized equipment to generate, inject, and detect the signature.
What is still needed in the industry is an effective, yet relatively simple and inexpensive method for detection of islanding in distributed power generation systems.